(defn get-notes-by-command
  "Returns a map: key is tick, value is set of notes that match given command at that tick"
  [grouped-notes-by-tick command-type]
  (reduce
    (fn [acc [tick notes-map]]
      (let [off-notes (command-type notes-map)]
        (update acc tick #(if % (conj % off-notes) off-notes))))
    {}
    grouped-notes-by-tick))
(get-note-offs grouped :note-off)

(defn get-first-note-tick
  "Given a note and ordered map of ticks to notes set, returns the first tick the note appears in"
  [note off-notes-map]
  (key (first (filter
                (fn [[tick notes-set]]
                  (contains? notes-set note))
                off-notes-map))))

(defn map-notes-set
  "Given an ordered map of note events, returns a map: key -> on_tick, value -> note::off_tick"
  [[tick note-sets] ordered-notes]
  (let [off-notes (get-notes-by-command ordered-notes :note-off)]
    (map #(map get-first-note-tick % off-notes) (:note-on notes-set))))

(defn pair-on-off-ticks
  [ordered-notes]
  (map #(map-notes-set % ordered-notes) ordered-notes))